This invention relates to methods and devices for carrying out immunodiagnostic assays. More specifically, the invention relates to methods and devices involving the use of chromatographic membranes, strips or gels through which sample, analyte, and reagents may move. The invention relates specifically to a chromatographic diagnostic test device for immunochemically determining the presence or amount of an analyte through the use of a multivalent mobile receptor particle and a trapping agent located in the path of moving sample, analyte, and reagents. More specifically still, it relates to a non-competitive assay through the use of a non-competitive trapping agent having a low affinity for unreacted receptor, thereby enabling the separation of bound from unbound receptor and enabling quantitation or semi-quantitation of the bound and/or unbound receptor.
The use of specific binding reagents has proven to be very useful in diagnostic assays and other applications. Such assays involve the detection and determination of an analyte in a sample by causing the analyte to selectively bind or react with a receptor capable of binding to the analyte in the presence of potentially interfering substances. These specific binding receptors form the basis for detection systems that are in widespread use in the art.
The visualization of the results of specific binding reactions is often facilitated by employing one member of the specific analyte-receptor binding pair in labelled form in order that the binding reaction may be indirectly measured by detecting the location and intensity of the label. Useful labels include radiolabels, chromophores, fluorophores, enzymes, magnetic or latex particles, and colloidal gold, the presence of which may be detected by means of various detectors such as gamma counters, spectrophotometers or the naked eye.
Immunoassay devices which generally include a chromatographic membrane, a sample receiving zone, and a labelled receptor for the analyte impregnated in the membrane are well-known in the art. In use, a sample liquid such as urine, blood, serum or other biological fluid suspected of containing an analyte is added to the device. The analyte in the sample reacts with its specific receptor and is captured. The capture event is manifested on the strip in a manner determined by its design and the location and type of reagents used in the assay. The presence or absence, but not the amount of analyte, is then determined by correlating the reaction with the receptor with some standard. Such assay devices properly configured can provide rapid and generally reliable results, but suffer from a variety of restrictions which limit their acceptability and widespread use.
In the field of diagnostic testing, the art has evolved from the use of complex radioimmunoassays and enzyme immunoassays to the use of single card or strip-type devices, either of a unitary, single piece type or having overlapping components. In general, the art has sought to increase the readability of such devices, to eliminate the need for instruments and to shorten the test time so that one may make a determination of the analyte under on-site conditions.
The art has also attempted to reduce the number of steps required to conduct the test to increase the simplicity and convenience of the system. Attempts have been made to produce semiquantitative, non-instrument based immunochemical assays for on-site use but such devices have not been satisfactory for various reasons. For example, they may not be economical to manufacture or the method might be too technique-dependent to be reliably performed by laboratory trained personnel, or the read-out may not be simple enough for on-site use, and/or sample collection. In addition, there often is a need for accurate measurement of volume applied sample when quantitative or semiquantitative results for on-site assays are required. The art would greatly benefit from a semiquantitative or quantitative assay which does not require any measuring of volume of sample, yet can be manufactured economically and provide quantitation of the analyte on the test device itself requiring no instrumentation or extrinsic reading assistance.